A typical car driven 20,000 km a year emits to the atmosphere about 11 kg per year

Question:

A typical car driven 20,000 km a year emits to the atmosphere about 11 kg per year of NOx (nitrogen oxides), which cause smog in major population areas. Natural gas burned in the furnace emits about 4.3 g of NOx per therm (1 therm 5 105,500 kJ), and the electric power plants emit about 7.1 g of NOx per kWh of electricity produced. Consider a household that has two cars and consumes 9000 kWh of electricity and 1200 therms of natural gas. Determine the amount of NOx emission to the atmosphere per year for which this household is responsible.